1. Field of the Invention
The present invention relates to a sputtering composite target, a method for manufacturing a transparent conductive film using the same and a transparent conductive film-provided base material. In more detail, the present invention relates to a sputtering composite target which is suitably used for manufacturing an indium oxide (In2O3) based transparent conductive film with low electrical resistance and good conductivity, a method for manufacturing a transparent conductive film using the same and a transparent conductive film-provided base material.
2. Description of the Related Art
There have hitherto been used In2O3 based (for example, In2O3—SnO2 based (hereinafter referred as “ITO”)) films as a transparent conductive film to be used for flat panel displays such as liquid crystal displays and plasma displays and so on.
These transparent conductive films can be formed as a thin film with low electrical resistance on a substrate by a sputtering process using, for example, a sputtering target having titanium added to ITO as a raw material. On that occasion, in order to enhance electrical and optical characteristics of the film, the formation of a thin film is carried out by heating a glass-made substrate at a high temperature of about 300° C. (see Patent Document 1, JP-A-2004-168636).
However, in the case where other components such as color films and inks are used for the substrate, those having a low heat-resistant temperature are included in these other components. Therefore, a process for fabricating a transparent conductive film without heating the substrate to a high temperature is demanded. Also, in particular, in the indium oxide system, additives to be doped or oxygen vacancies largely affect conductive carriers. Therefore, research and development are being widely conducted from both the material standpoint and the process standpoint.
For example, as for an indium tungsten oxide thin film, by specifying a composition ratio of constitutional materials, it can be fabricated by heating a substrate at a relatively low temperature as 150° C. (see Patent Document 2, JP-A-2002-256424). Also, as for an indium zinc oxide thin film, there are disclosed a method of obtaining a good transparent conductive film by subjecting an obtained transparent conductive film to a heat treatment on a substrate at 200° C. in an oxygen or hydrogen atmosphere (see Patent Document 3, WO 04/105054); a method of doping aluminum or gallium to form a film and then subjecting the film to a heat treatment at not higher than 300° C. in a reducing atmosphere, thereby lowering the electrical resistance (see Patent Document 4, JP-A-2000-44236); and a method of adding a hydrogen gas in a sputtering gas and then performing a heat treatment at from 80° C. to 180° C. (see Patent Document 5, JP-A-2002-343150).
Furthermore, it is investigated to control the electrical resistance and stability by performing a treatment for the purpose of introducing oxygen vacancies in a sputtering process and steps before and after the sputtering process.
For example, as for those for focusing on a preparation method of an ITO target, there are disclosed a method in which in addition to indium oxide and tin oxide, metallic indium and metallic tin are added at the time of preparing the ITO target to regulate the oxygen content in the target at from 8 to 17% by weight, and oxygen vacancies are introduced into a thin film after the fabrication (see Patent Document 6, JP-A-05-222526); and a method in which a sintering step at the time of preparing the ITO target is carried out in vacuo or in an inert gas atmosphere or reducing gas atmosphere, thereby lowering the oxygen content in the target (see Patent Document 7, JP-A-03-44465).
Besides, as a method of obtaining an ITO thin film with low resistivity at a low temperature, there is disclosed a method in which in a DC magnetron sputtering process, energy of a molecule to be sputtered in reaching a substrate and a fabrication rate are optimized by controlling a bias voltage and a target current, thereby obtaining a thin film with low resistance under a condition under which substrate materials are placed at a relatively low temperature as not higher than 40° C. (see Patent Document 8, JP-A-2006-117967)